1. Field of the Invention
The invention relates to a method of detecting cardiac interval signals in cardiologic devices, in particular of detecting tachycardiac arrhythmias, comprising the following method steps: time-resolved detection of cardiac events which are representative of the cardiac interval; determination of the respective cardiac interval between two successive cardiac events; statistical evaluation of a certain number of successive cardiac interval values.
2. Background Art
From relevant technical devices, for instance cardiac pacemakers used to combat tachycardiac arrhythmias, it is known to detect cardiac events of the monitored heart by special detection methods, to subject the measuring results obtained therefrom to corresponding evaluation criteria, and, based thereon, to determine corresponding therapy deliveries to the monitored heart, for instance in the form of electric pulses, by the aid of suitable algorithms. Cardiac events to be used are for example the stimulus signals that occur during atrial and ventricular contraction of the heart, which are representative of the cardiac intervalxe2x80x94the time interval between two contractions of the heart.
Atrial and ventricular heart rates or intervals and the comparison thereof can be used among others as a criterion for the existence of tachycardiac arrhythmias.
For evaluation implementation in prior art cardiologic devices, it has been known to make use of the cardiac events which are representative of the cardiac intervals and are detected in time resolution, in order to determine the respective heart interval between two of these successive cardiac events. A certain number of successive heart interval values are then statistically evaluated so as to suppress, to a certain degree, faulty measurements. For instance, a so-called xe2x80x9cx out of y controlxe2x80x9d is carried out, in which defined events are used as a basis for the determination of suitable therapy deliveries in the cardiologic device only when they have occurred x times out of y detections.
In connection with the detection of tachycardiac arrhythmias, sliding averaging is standard for the statistical evaluation, in which a certain number of successive cardiac interval values are subjected to continuous averaging. When atrial and ventricular events are used in practice for heart interval determination, the continuously detected atrial and ventricular averages of the cardiac interval values are compared with each other, significant deviations of these averages from each other and defined behaviors of successive averages suggesting to certain arrhythmias. Based on the detection specified above, corresponding therapy deliveries to the monitored heart are then detected in accordance with given algorithms in the control of the cardiologic device. These sequences, a very abstract idea of which has been given above, are put into practice by correspondingly programmed algorithms in the microprocessor based control systems of today""s cardiologic devices.
Of course, faulty measurements may occur during the detection of cardiac events. For example, so-called xe2x80x9cundersensingxe2x80x9d or xe2x80x9coversensingxe2x80x9d can be found in the detection of atrial and ventricular events. xe2x80x9cUndersensingxe2x80x9d is the faulty non-detection of atrial or ventricular events that have really taken place. xe2x80x9cOversensingxe2x80x9d is a faulty measurement, in which a pulse is detected without any corresponding atrial or ventricular event having taken place.
In cardiac interval determination, single atrial or ventricular xe2x80x9cundersensingxe2x80x9d has the effect of doubling the heart interval value determined therefrom. In a statistic evaluation in the form of averaging of for example four successive heart intervals, the faulty measurement enters four times in succession into sliding averaging. Consequently, the real heart interval is not correctly determined four times in succession, whichxe2x80x94in particular in the case of repetitionxe2x80x94may give rise to inadequate therapy delivery by the cardiologic device, entraining corresponding risks for the patient.
It is the object of the invention to improve the method of detecting cardiac interval signals such that individual faulty measurements are recognizable and correctable in particular with a view to the statistical evaluation of successive cardiac interval values.
This object is attained in that along with the statistical evaluation of the certain number of successive cardiac interval values, an individual comparison of this certain number of cardiac interval values with one another takes place in such a way that individual cardiac interval values, which significantly deviate from cardiac interval values that occur there-before or there-after, are recognized as faulty measurements and correspondingly corrected.
The method according to the invention profits from the knowledge that in the detection of cardiac interval signals, faulty measurements will occur as so-called xe2x80x9coutliersxe2x80x9d, which are characteristic individual events. Such an individual event becomes recognizable by a continuous comparison of successively detected heart intervals in particular in a retrospective view and, based on the storage capacities of the microprocessor based control systems of nowadays cardiologic devices and implants, it can be employed for a corresponding correction of the cardiac events from which to determine therapy. Preferably in the case of superimposed statistical evaluation and correction of the detected heart interval values, the heart intervals which have been evaluated statistically can be corrected subsequently upon recognition of a faulty measurement.
Statistic evaluation on the basis of sliding averaging preferably makes use of at least four successive cardiac interval determinations. Preferably, the individual comparison of the heart intervals with one another for the recognition of faulty measurements then takes place, based on a number of cardiac intervals which is identical with the number of cardiac interval determinations used for averaging.
Further preferred embodiments of the method according to the invention involve special method steps dealing with faulty events in the case of the mentioned xe2x80x9cundersensingxe2x80x9d and xe2x80x9coversensingxe2x80x9d during the detection of atrial or ventricular events. Details of this will become apparent from the ensuing description of an exemplary embodiment of a method according to the invention, taken in conjunction with the drawing.